A critique on Veizer’s Celestial Climate Driver

In a paper in Geoscience Canada, Veizer (2005) states that ‘the multitude of empirical observations favours celestial phenomena as the most important driver of terrestrial climate on most time scales‘. This paper was cited by a contributor to a debate on the website openDemocracy . In short, the argument is that the cosmic ray flux (CRF, also denoted as ‘GCR’ – galactic cosmic rays – in some papers) is the most important factor affecting our climate. Since this issue is likely to crop up from time to time, it is worth taking a closer look at the Veizer (2005) paper ( Here is a link to short summary, but the actual paper requires subscription). [Update: The actual paper is now available as supplemental material on the Geoscience Canada website.] I will try to show that CRF explanation for the recent global warming is easy to rule out.

One of the main planks of the argument that CRF is responsible for the most recent warming is based on figure 14b in Veizer (2005), where there appears to be a trend in CRF from eg Climax neutron monitor (also, see plots at this URL). This CRF-curve was a surprise to me, and furthermore, it’s at odds with CRF-evolution presented in figure 17 in the very same paper (showing no systematic change) – how can these accounts be so different? The inconsistency becomes even more apparent when it is argued that the ‘balloon and satellite data ([Veizer, 2005] Fig. 17) do not show any clear temperature trend… Instead, their interannual temperature oscillations correlate clearly with … CRF’ (p. 22, 2nd column). Again, no long-term trend in the CRF-data. It has been argued earlier on RealClimate that there is no long-term trend in the modern CRF measurements. The lack of systematic trends in CRF and other solar activity proxies is well-known and published in the scientific literature (eg. Richardson et al, 2002). In fact, the CRF curves presented by some of the key cosmic-ray hypothesis proponents, Marsh & Svensmark, do not exhibit any trend, yet it has been claimed that CRF is responsible for the most recent warming (Marsh & Svensmark say that the wiggles correlate, but don’t discuss the [or lack of] observed trends).

There are other aspects which appear as problematic for the CRF-interpretation for the recent global warming. First of all, according to IPCC (2001) the night-time temperatures have in general increased more than the day-time temperature (the diurnal temperature range, DTR, has decreased in most areas, except over middle Canada, and parts of southern Africa, south-west Asia, Europe, and the western tropical Pacific Islands). Since individual clouds have a life time of hours, and the CRF-interpretation involves changes in the reflected light as well as ionisation, a climatic response from change in CRF is hypothetically almost instantaneous, and it is a challenge to explain why the night side (where there is no sunlight and hence reflection cannot play a role) warms more strongly than the dayside, if the CRF were to drive the recent warming trend. Another equally important challenge is the fact that there are pronounced ~11-year variations in the CRF, but the presence of ~11-year variations in the global mean temperature are much less pronounced than the trend over the 3–4 most recent decades. If the CRF were so important (and the cloud response near-instantaneous) why do we not see more pronounced ~11-year variations in the global mean temperature?

The paper also gives the impression that there is no trend in satellite-based temperatures (MSU), which is wrong. There are various analyses of the satellite trends, all of which indicating a warming trend in the troposphere.

When Veizer summarises in bold type face ‘(above) empirical observations on all time scales point to celestial phenomena as the principal driver of climate’, he neglects to discuss the fact that the stratosphere has been cooling, which at higher levels is consistent with an enhanced greenhouse effect (most of the cooling in the lower stratosphere is related to changes in ozone) but inconsistent with enhanced solar activity and his CRF-hypothesis. Another argument Veizer uses to support his hypothesis is that the correlation between the proxy indicators for CRF is better correlated with ‘climate’ than between CO2 and climate. Yet he does not provide any references or justify his argument. I find this statement rather puzzling, as it seems to me that there is a good correlation between the CO2 and temperature proxies such as can be seen in Veizer’s own figure 7. The same seems to be the case in Fig. 1 below:

Fig.1: A comparison between CO2 and CRF indices with temperature proxy. Superimposed is the Beryllium-10 (blue). All curves are standardised. (paleaoproxy.R).

If we’re looking at the last century, then there is a sulphate aerosol “blip” that worsens the CO2-T correlation. But there are also times when there are distinctive features in the CRF proxies in Veizer (2005) figure 8, when there is no corresponding response in the temperature (figure 7 of Veizer, 2005). Actually, I do not see much resemblance between the CRF-proxies presented in the paper and the temperature proxy, and there is no quantitative statistical analysis of their correspondence. Thus, the above statement appears to be a value judgement, rather than an objective observation. Along the same vein, the paper claims there is a good degree of correspondence between the timing sunspot minima and minima in precipitation curves in Veizer (2005) figure 16. I do not find his (hand waving?) arguments convincing. Note, the paper does not offer any quantitative statistical analysis on the correspondence of these curves. Nor does it discuss how the CRF-proxies may have been affected by past variations geomagnetic field, which clearly would degrade any correlation between CRF and climatic indices. It should be noted that proper attribution studies don’t just do correlations, they are rather more sophisticated. There is the possibility of the presence of a common cause that may have affected the various isotope records (representing both CRF and ‘climate’), and Veizer does not even mention the possibility that the deposition efficiency of these may be affected by climate itself (e.g. circular reasoning).

At other times, the discussion misrepresents the current knowledge when comparing only the clouds’ albedo effect with the CO2 forcing, and not the net effect including the absorption of long-wave radiation (p. 14, 2nd cloumn). The Veizer (2005) paper also tends to make strong statements based on controversial papers (eg. Soon and Baliunas, 2003; p .20, 3rd column – several editors left the journal after it was published because they felt it was flawed). I find Veizer’s reference to other work very selective. The role of CRF as a driver for climate is indeed controversial, and this fact is not acknowledged in the paper.

On a more technical note, an R-script gcr.R is available from this site which helps you retrieve the CRF-data over the Internet and plot the data. Please use it, play around, and see for yourself. Another script, paleaoproxy.R is also available here, and is makes Fig. 1 above.

30 June 2005

Addendum: “Celestial Driver” Part 2

In the above post, time permitted us only to discuss a few of Veizer’s arguments, focussing mainly on the cosmic ray flux. Here we take a look at some of the other arguments presented in his paper.

Solar cycle length
Veizer suggests the recent global warming might be driven by changes in solar activity (his Fig. 14a – dashed line is temperature, solid line with diamonds is solar cycle length). But the figure only shows the temperature record from 1935-1990, even though of course more recent data are available. Veizer must be aware that in view of these more recent data, the scientist who originally proposed this correlation in 1991, Knud Lassen, has concluded in 2000 that solar cycle variations cannot explain the ongoing warming trend [1].
In the figure below, we have superimposed the standard CRU data set (blue curve) of global mean temperature on Veizers graph.

We see that the graph selectively shows a part of the time series dominated by the well-known temporary “dip” in the global warming trend, reaching a minimum around 1970. The correlation of temperature and solar cycle length applies mainly to this “dip” in the curves. Thus, solar cycle variations may or may not explain this “dip” (one similar-looking dip in two curves is not a significant correlation and could easily be coincidence; there is a better-founded explanation for this “dip” resulting from cooling by aerosol emissions – see the figure from Hansen et al. coming up below).

But there is no indication that solar cycle variations could explain the ongoing warming trend. There is simply no significant trend in this (or any other) solar indicator since 1940. Veizer fails to discuss the key issue (namely, whether the data support the idea that the warming trend, rather than just the temporary dip, could be explained by solar cycle variations). The (often faulty or misleading) use of these solar cycle data by “climate sceptics” has quite a pre-history, see e.g. Damon and Laut (2004). Note that the relative vertical scale of the curves is arbitrary. The article by Damon and Laut (2004) also shows that when solar cycle length is scaled up as much as it is in the above figure in order to match the 1940-1990 temperature record, that this implies a great mismatch for the earlier periods in time. Veizer should be aware of this problem of his proposed match, but he fails to mention it.

As an aside, one of the data points in the above graph is incorrect; the National Geophysical Data Center gives a solar cycle length of 11.8 years for 1963, where Veizer plots 11.0 years.

Greenland temperature variations
Veizer’s paper argues that the local preindustrial climate fluctuations over the past millennium in Greenland were not driven by CO2. As a proof, Veizer shows a temperature reconstruction for Greenland together with the CO2 concentration in his Fig. 12. Now, the preindustrial CO2 concentration over this period was constant, and therefore nobody has ever proposed that CO2 could have caused any climate variations during this time. It obviously can’t. Showing this in a plot is thus a completely moot point that is clearly not aimed at any fellow scientist; it is something meant to impress uninformed lay-people. Indeed, the graph is not from a scientific publication, but was reproduced from a popular climate-sceptics book that has been distributed in Germany by the coal-industry lobby.

Using a time period when CO2 did not change at all, to support a general conclusion that “CO2 is not the driver of climate change” and hence is not responsible for the current warming, is hardly logical. It merely highlights the fallacy of looking for one single “driver” that explains climate variations on all time scales. It is well-established in climatology that different causes and mechanisms have caused climate changes in the past (orbital variations, plate tectonics, solar variability, volcanic eruptions, etc.), so that a cause-effect relationship has to be determined for each individual case, rather than looking for one overall “driver”.

(As an inconsequential but telling aside, Veizer wrongly attributes the CO2 curve in Fig. 12 to the Greenland ice core GISP2. It is well-known amongst paleoclimatologists that there are no successful CO2 measurements from Greenland, the record shown is obviously from Antarctica. It is strange how this slipped by the journal’s review.)

A strange temperature graph
Veizer publishes the above graph to suggest that temperature and CO2 concentration do not look alike, hence CO2 has not caused the warming.

First, Veizer’s temperature curve looks unlike anything published in the scientific literature. Temperature in the year 2000 no warmer than 1960? Clearly something is wrong with this – seemingly hand-drawn – graph. It is once again not a scientific diagram but lifted from the german climate sceptics book “Klimafakten” mentioned above. It is remarkable (and perhaps a novelty in the history of science) that the paper takes several graphs straight from climate sceptics PR material produced for lay-people, rather than basing its case on peer-reviewed scientific sources. It is surprising that the faulty temperature graph – which sticks out like a sore thumb to any climatologist – could slip through the review procedure at Geoscience Canada.

Second, this is a very naive argument. CO2 has increased in a smooth trend, hence it can obviously only explain the overall trend in the temperature data, but not any shorter-term variability around this trend. Nobody has ever suggested it should, thus this graph is another moot point clearly not aimed at scientists.

The observed temperature evolution can of course only be the result of all forcing factors combined (including solar variability, volcanic eruptions, and man-made aerosols) – not CO2 alone. If all these forcing factors are taken into account in a recent model simulation, the temperature evolution looks like this:

The black line is the average of five model runs. This is not only in excellent agreement with the observed temperature changes at the surface (blue stars), it also correctly reproduces the observed heat storage in the oceans – a strong indicator that the model’s heat budget is correct. The agreement of this model with observations is particularly good and perhaps partly fortuitous, given that there is still uncertainty both in the climate sensitivity and in the amplitudes of the aerosol and solar forcings. But our main point does not depend on that and is robust: with any model and any reasonable data-derived forcing, the observed 20th Century warming trend can only be explained by anthropogenic greenhouse gases, while other factors can explain the shorter-term variations around this trend. The serious scientific discussion is about the exact contribution of each factor, not about identifying one single “driver”.

Is the CO2 increase anthropogenic?
In this paper (as in the past) Veizer is strangely vague on the question whether the recent CO2 increase in the atmosphere – which is at the very core of global warming concerns – is caused by humans. He claims that the “carbon cycle is piggy-backing on the water cycle”, and he states that “while CO2 may act as an amplifying greenhouse gas, the actual atmospheric CO2 concentrations are controlled in the first instance by the climate, that is by the sun-driven water cycle, and not the other way around.”

Veizer’s alternative hypothesis for 20th century global warming does appear to be: the warming was caused by a “celestial driver” (i.e., a change in solar activity – despite the lack of observed trend), and it is this warming which has increased the CO2 concentration, not the other way round.

If this is Veizer’s hypothesis (and we welcome his clarification if we have misinterpreted it), then this is indeed radical. That humans have caused the increase in CO2 is proven beyond reasonable doubt, and is generally accepted even by “climate sceptics”. We have summarised the evidence here. Not only do we know how much CO2 we emitted (more than is now left in the atmosphere – which means that the natural reservoirs have taken up part of our CO2 emissions, rather than having released CO2 in response to a climate change). That the increasing amounts of CO2 in the atmosphere come from fossil fuels was already demonstrated by isotope analysis in the 1950s. CO2 increases not only in the atmosphere but also in the global oceans – this is documented by 10,000 measurements – and very likely in the biosphere. And it would be difficult to argue that through a natural climate change, CO2 has suddenly increased to values about 30% higher than at any previous time for the past 650,000 years, and that this occurred by chance just at the same time as humans released more than enough CO2 to explain the rise.

In the light of this evidence, it is difficult to believe that Veizer means to suggest the CO2 rise is a response to a natural warming. So perhaps Veizer does agree that the CO2 rise is caused by humans? Then it logically follows that Veizer also agrees there must be anthropogenic warming, since Veizer does agree to that basic fact of physics: that CO2 is a greenhouse gas – see his quote above.

Some final remarks
It is a normal, essential and very valuable part of science to develop and present alternative hypotheses, even if they appear unlikely at first, go against the mainstream, or turn out to be wrong later. Without this process, there would be no progress in science. Hence, any attempt to find an alternative explanation for the ongoing global warming is to be welcomed.

However, to facilitate this process, science has developed a culture with certain rules and standards for scientific discourse. These rules include, for example, that all relevant data are shown: if I want to make a credible case for any hypothesis, I must not hide parts of a data set which do not fit my hypothesis. Rather, I need to discuss them. In a scientific paper, a selective or misleading graph may be of little consequence (except for the author’s reputation), as scientific readers are familiar with the further data and the previous scientific discussions, so they can easily judge the merits of an argument. However, it is in our view more serious and ethically questionable when such selective and misleading use of data is made in a press release: an example from a media release by Veizer / Ruhr University is discussed here.

21 Responses to “A critique on Veizer’s Celestial Climate Driver”

Rasmus. You wrote that “There is the possibility of the presence of a common cause that may have affected the various isotope records (representing both CRF and ‘climate’)”. It is worth alerting our readers that this isn’t merely a possibility, but a well established fact! For the Vostok, Antarctica, record shown in Figure 1, we know that the reason 10Be concentrations increase when the temperature indicator decreases is that the 10Be flux has been diluted by lower snow accumulation rates characteristic of colder climate. This has been well established since at least 1989, when Jouzel and others pointed it out in a paper in Quaternary Research. Every study of 10Be since that time has backed this up. For example, the GISP2 ice core record from Greenland similarly shows an approximate doubling of 10Be concentrations during the last glacial period when we know with 100% certainty that accumulation rates of snow had halved, demonstrating that there was no change in the 10Be production rate and therefore no change in the cosmic ray flux. – eric

As background to this topic, a good paper to read is C02 and Climate Change by Crowley and Berner, Science vol. 292 (5518): 870-872 , 4 May 2001. The dispute concerns:

As discussed by Veizer et al. there is a major discrepancy during the mid-Mesozoic (120 to 220 Ma) between cold low-latitude temperatures deduced from the oxygen isotopic composition (Î´18O) of fossils and high levels of CO2 and net radiative forcing. The low-latitude Î´18O data are at variance with other climate data that show high-latitude warming and an absence of large-scale continental glaciation….

The persistent Phanerozoic decorrelation between tropical Î´18O and net radiative forcing demands a more comprehensive explanation….

The point being that these very ancient discrepancies exist but, as noted in the post (follow the “controversial” link) the correlation with CRF over geological time with temperature as measured by proxy data has not been established. Certainly, there is no reason to believe that CO2 as a climate driver has been undermined in any way, especially on shorter time scales.

You say:
“… The role of CRF as a driver for climate is indeed contriversial, and this fact is not acknowledged in the paper.”

“Indeed controversial” is academic language; but to politicians, this sounds like ‘praising with faint damnation’ — a politician is apt to assume “is indeed controversial” means “is a hot research area” rather than “was asserted in one paper that used at best controversial methods to reach its claimed conclusion” — eh?

Oh — and check the spelling — “contriversial” looks like either a Freudian typo or an intentional pun. Maybe it’s a legitimate word for contrived results — I’m far out of touch with academic jargon (grin).

I would be interested to know what you think of a model by a professor in my department, Bose Nordell. His main point is that all the fossil fuels we use heats up the earth since we are using ‘trapped’ energy.

Thanks for the info people.
Can I point out that ultimately we need to build sustainable systems if we are to consider our survival as a civilisation into the future. These arguments, while worthy and interesting, do not effect the imperative of our current situation. Burning fossil fuels and nuclear power are both limited in duration and polluting and therefore unsustainable. We need to get it right and if there is any question of environmental damage we need to do it now. For info on how you can personally do this easily see http://www.yeswecandoit.org

Hi again and thanks for the editing… but the question is more complex then the answer on that other blog, but I understand if you don’t have time to look in on it.

[Response: I did take a look at the paper and William is correct: This can’t be right. As the comment from Covey et al makes clear, he is calculating a sensitivity to surface energy fluxes that is almost 100x larger than standard estimates of the climate sensitivity. This is most likely because his radiative model does not have any atmospheric mixing, and therefore the response to near-ground fluxes is hugely overestimated. The basic comparison should be with the net forcing (around 1.8 W/m2 from GHG, solar, aerosols etc.) and the 0.02 W/m2 from thermal pollution. The latter is negligible. -gavin]

[Response:There is some discussion of the paper, finding its results implausible, on the newsgroup sci.env – William]

The questions on the CRF-climate link are legitimate. Recent sun-cloud connections have a decreasing correlation with CRF, but a good correlation between (low) clouds and solar irradiance, see figure 1 in http://folk.uio.no/jegill/papers/2002GL015646.pdf
Also in the 6 May 2005 Science, there is an article which finds a long-term link between solar intensity (based on 14C variations) and monsoon intensity over the past 9000 years…

Still, while there are several theories, there is no direct proof of what physically drives the sun-climate connection. What is clear, is that the influence is larger than what is mostly included in current models as direct insolation only.

Further, in more recent times, there is a very close CO2-temperature relationship in the Vostok (and other) ice cores. But there is a lag of CO2 after temperature of some 600 years during deglaciations, and several thousands of years during the onset of new ice ages. While the overlap during deglaciations is large (which makes it near impossible to make any estimates of relative forcings), during the start of the last ice age, there was no overlap: CO2 started to decrease (some 40-50 ppmv) when the temperature was already near it’s minimum. See: http://www.ferdinand-engelbeen.be/klimaat/co2_temp_ice.html
A later correction by Vimeux e.a. (last page/graph for Vostok) of the deuterium/temperature trend did change the amplitude of the temperature variation, but not the timing. The long lag of CO2 is probably not the result of timing errors between ice age and gas age in the ice core, as methane more closely follows the temperature record (for the timing, see also the discussion at UKweatherworld).
This means that a change of 40-50 ppmv of CO2 has no measurable effect on temperature… That doesn’t mean that there is no effect at all, but it is smaller than implemented in current models.

If one looks at all recent pre-industrial time scales, one sees either a lagged overlap between CO2 and temperature or a lag where CO2 follows temperature. That was the case for the 8.2 ka event (stomata data), the Taylor Dome for last millenium (temperature data not present anymore) and even during recent times: CO2 increase variations follow sea surface temperatures (El NiÃ±o) superimposed over the industrial trend…

[Response: Ferdinand, in your response to one of our earlier posts, you said something about the Law Dome data having “disappeared from the internet”. In this post you say the same about Taylor Dome. I suspect you mean Law Dome, but in any case I would be surprised if data from one of the National Data Center’s is no longer available. Can you clarify? What data sources are supposedly no longer supplying the data? – eric ]

Thanx for taking time, I’m a bit out of my field here… I’m an “environmental” engineer specializing in geochemistry… but I try to read al the news on climate changes and GHG since it really interests me

and btw, this work by Nordel is done on his spare time and by students, he has not had any resourses for research yet…

I’ve read the paper by Bo Nordell and it is junk. Here is as summary I wrote in sci.environment after having read it:
“The difference between the surface of the Earth and space is 33 degrees.
Geothermal heat produces about 0.07 W/m^2 heat. and if this causes 33
degrees heating the climate sensitivity must be 470 K/W/m^2. Thermal
pollution is 0.02 W/m^2 and will thus give a heating of 0.02*470= 9 K.
The mathematics he uses reduces this by a factor of 3, but essentially
this is his argument.”
To Nordell the sun seems to be just a small inconvenience, not the source of the greenhouse effect.

The paper does in a way fit in this thread. Just like astrophysicists starting to study climate tends to blame everything on the sun, Bo Nordell who works on extracting heat from boreholes see everything in that perspective.

[Response:Thanks Thomas. I’ve written a bit more about this here, which will point you to replies to Nordell just published in the same journal, if you haven’t seen them already – William]

Yes, I agree with many of your remarks. The bulk of the evidence points toward CO2 as an amplifying feedback, not a driver during the Ice Ages. Caution is warranted for even longer time scales.

However, the constructed CO2/temperature graph (Geocarb III/Paleomap) in your first link is highly suspect; the graph reconstruction is much too precise and does not reflect large uncertainties in the data. Look at the results at CO2 as a primary driver of Phanerozoic climate for example, especially figures 1 and 2 (GSA Today, March 2004). I can only conclude that the graph was constructed to score some political point.

As I said, there are certainly CO2/Climate discrepancies in the Phanerozoic data. Given the enormous uncertainties (for continental configurations, ocean currents, amount of volcanism, etc) in reconstructing these records, it would be suspicious and surprising if there were not such mismatches. Reconstructing ancient carbon cycles is really hard to do and once again climate models using the best available proxy data are our best bet. Most scientists working on this do conclude, however, that there is a reasonable 1st order approxmation between CO2 and climate.

Finally, as all this relates to the post concerning the work of Veizer: no Phanerozoic correlation (let alone attribution) has been established with respect to CRF/GCR. If this premise is not established, nothing further can be said about what’s going on now during our unsupervised perilous experiment with Earth’s climate. It appears that CO2 levels have not been this high since the Eocene. And as Rasmus shows, it is straightforward to demonstate that CFR is not the cause of industrial age warming.

[Response: Readers interested in the question of CO2 lag/lead vs. temperature should read J. Severinghaus’s post, one of the first ones up on RealClimate, here. –eric]

Indeed it was Law Dome, not the Taylor Dome… I had written that from memory, but as my memory is not anymore what it was 40 years ago…
What I meant was a graph on the Internet, showing the Law Dome ice core CO2 variations, lagging the temperature variations with some 50 years (with ~10 ppmv/K, similar to the factor found over the Vostok ice core trends). But all graphs now only show the CO2 variations and the NOAA databank only contains the CO2 data. I haven’t found the temperature data anyway, which might be of interest to see the CO2-temperature lag, while it seems that the temperature data were calculated (see: IPCC: “Recent series obtained at Law Dome, another coastal site of East Antarctica, show instead a cold reversal preceding the Younger Dryas as in other Antarctic records”. But it is possible that the graph was a mix of CO2 data from Law Dome and temperature data from a different site/proxy.
Btw, there is a lot of discussion between stomata researchers and ice core researchers nowadays. Stomata data show a much larger variation of CO2 in the last millenium (besides higher values in general), in part caused by the smoothing effect of relative slow closing air bubbles in ice cores…

What really disappeared from the NOAA database is the temperature reconstruction of China, which I had downloaded from there. Similar trends for China can be found in stalagmite data graph # 3…

Just wanted to check. This paper was peer reviewed? Cause the mistakes you describe are ones you would expect peer review to catch. I guess it depends on which peers do the reviewing and how much time they spend.

[Response: We were wondering about this as well. As it turns out, the two reviewers of the journal are named in the acknowledgement, and they are both not climatologists. (Unusual that they did not do an anonymous review, and interesting what the author thanks them for.) That explains why those errors were not caught. But it raises the question why the journal chose to have a highly controversial (to say the least) paper on climate change reviewed only by non-climatologists. Imagine someone writing a paper claiming smoking is not harmful, reproducing unscientific PR material from sources close to the tobacco industry, and the paper not even being reviewed by a cancer expert but by a dentist and a vet! In my view, this is fully analogous to what happened here. -stefan]

I will try to show that CRF explanation for the recent global warming is easy to rule out

and comment #12 states that

…it is straightforward to demonstate that CRF is not the cause of industrial age warming.

These are incorrect statements. What you present are some issues that a CRF theory (maybe) has to explain. That is something completely different than showing that it is easy to rule out.

[Response:I show that there is no proof supporting the notion that CRF is responsible for the most recent global warming. On the background of our physical understanding and the empirical data – i.e. the lack of trend in the CRF record (as well as other solar proxies such as 10.7 cm flux) – the notion is inconsistent with our understanding of how the world works. The hypothesis proposed by Svensmark and others is that the CRF affects the ionisation of aerosols and the number of cloud condensation nuclei (CCN) , which again affects the fraction of low clouds and the planetary albedo. This implies that the CRF levels must have systematically decreased over time, causing a long-term decrease in the low cloud fraction and hence a long-term reduction in the planetary albedo, that again would be responsible for the warming. This explanation is definitely at odds with the empirical data, and according to Carl Popper, falsified. Could there be other explanations for climate change, involving CRF? Perhaps, but new hypothereses must be postulated before they can be tested. Thus, we can only falsify known hypotheses and it’s impossible to test the unknown. -rasmus]

RE #9, that CO2 may be lagging (or caused by) warming should not give anyone solace. We know that GHGs, including CO2, naturally keep earth warming, so it is reasonable to expect additions of GHGs into the atmosphere would increase that warming even without evidence & we do have increasing levels of evidence. Now, if warming also causes increased CO2, then we may be talking about a positive feedback loop in which the warming spirals upwards, which amplifies the warming effect of whatever CO2 we humans contribute to the atmosphere.

Lynn, there is no doubt that CO2 is a greenhouse gas and the extra addition by humans will give an extra warming. The discussion is about how much that will be, or the difference between a benign warming and a disaster.

Therefore it is of interest to know what the influence of temperature on CO2 and vv. was in pre-industrial times. What we have seen – until now – is that CO2 always lags temperature changes, never leads, be it that there are large overlaps in most cases and sometimes synchronism. And that a change of 40-50 ppmv CO2 had no measurable influence on temperature (during the onset of the last glaciation), while several models imply that CO2 was responsible for halve of the change in temperature (or halve of the 8 degr.C for 80 ppmv increase in CO2 at the onset of the last deglaciation). But as CO2 acts the same for both ways (cooling and warming), either current climate models overestimate the (historical) role of CO2, or the measurements need some correction.

Dave, thanks for the links (especially the Berner one). They reveal the close relation between CO2 and temperature (within the error margins of all the proxies), but don’t solve the height of the influence of one to the other. Methane may be a different story, as that induces water at (near stratospheric) heights.

Eric, I had no possibility to react on Severinghaus’ point that Cuffey and Vimeux have solved the lag of CO2 after the temperature drop during the last glaciation, because the discussion was already closed. In fact, Cuffey and Vimeux did not solve the lag, they only corrected the temperature derived from deuterium/hydrogen ratio, which gives a more sinusoidal curve for temperature changes (and a better correlation between CO2 and temperature), but it didn’t change the timing: CO2 starts to decline, some 1000 years after the temperature reached it’s minimum.

[Response:If it were indeed true that CO2 always lags temperature changes, never leads (which I don’t believe) then what you would have proved is that past analoges are of limited value to assessing the present warming, because in this case we do know that the forcing if from GHG’s, since we know the CO2 increase is anthro – William]

Dear colleagues, I believe it would be only fair to add the folloving to the “critique” of Veizer as his response:

It would be a relatively easy task to compile a lengthy list of model deficiencies and failings, but because I appreciate the fact that progress in science is incremental, I prefer not to do it. It is my firm belief that the climate debate will ultimately be decided by the merits of the most logical case, not by the demerits of the alternatives or by personalisation of the discourse and advocacy. I only ask that those researchers that wish to arrive at their own judgement of what is it that I am really saying can do so by reading the entire article in its context (available under supplementary material). Please note that is my personal preference to confine any further discourse to scientific ways and means.

[Response:I totally agree that outcome of any scientific debate should not be done by demetits or personalisation of discourse and advocacy. I have tried to make it clear that this post was a critique of the paper and the hypothesis of a Celestial driver, not a personal criticism. But at the same time, it’s important to keep in mind that science is a ground on which trial and error over time leads to progress, and it would be wrong to discount wrong hypotheses all together as completely worthless – they do also play a role in this setting by providing a kind of ‘dynamic force’ and keep the debates going. Even protagonists of ideas that over time turn out to be wrong deserve some credit in my opinion. If I kept the post completely anonymous, wouldn’t I rob you of this credit? Besides, giving proper reference is important so other scholars know exactly what I’m talking about. But in the end, it’s the combination of empirical evidence and logical reasoning that must decide between conflicting explanations. The reader would definitely benefit from having access to the entire article, and thanks (to Veizer and editor of Geoscience Canada) for making your entire paper available for the RealClimate readers! (you may need to scroll down the page in order to find it) -rasmus]

GCR’s, Clouds, and Climate, Oh My!
If you were at a BBQ with a group of atmospheric scientists, and wanted to raise some hackles, there are several subjects that are notoriously easy to get people riled up… …Talk of Hockey Sticks, Inhofe, Crichton, Coulter, and you’re …